SEATTLE -- Like most NFL backups, Drew Lock doesn't get regular reps. But he visualizes plays by drawing Xs and Os on a whiteboard in his bedroom. When not memorizing Brian Fleury's playbook, it's covered in his son's scribbles.

That whiteboard may get more use with Sam Darnold out. Darnold suffered a hip injury in the opener against the New England Patriots. Coach Mike Macdonald said test results brought "really good news," but a source told ESPN's Adam Schefter that Darnold is expected to miss time. Lock likely starts next Sunday, Sept. 20, when the Seahawks open NFC West play at the Arizona Cardinals (4:25 p.m. ET, Fox), and potentially beyond.

Lock went 16-of-22 for 187 yards, one touchdown, and no turnovers in relief. His clean performance, plus three takeaways by Mike Macdonald's defense, helped Seattle rally for a 13-10 win at Lumen Field.

"He did a phenomenal job," said wide receiver Cooper Kupp. "He basically took no reps with any of the guys that were out there all week. You can see the onus that he puts on himself to be ready."

What would have been Lock's first touchdown pass -- a 7-yard throw to Kupp -- was nullified by an illegal shift. It was one of seven offensive penalties for the Seahawks. But Lock still delivered, hitting Jaxon Smith-Njigba for a 21-yard gain on third-and-22.